The present invention relates to a rotating disk storage device such as a magnetic disk drive or a magneto-optic disk device and, more particularly, to a mechanism for cushioning a shock imposed on an actuator and causing the actuator to stop at a retracting position upon abutment of the actuator against a stopper at a higher speed than usual due to, for example, external shock, runaway, or cut-off of power supply in a rotating disk storage device.
In a magnetic disk drive, a head/slider supported by an actuator assembly moves pivotally in an approximately radial direction of a rotating magnetic disk while flying over a recording surface of the magnetic disk through a slight spacing from the recording surface to read and write data. A load beam which supports the head/slider produces a pressure in a direction in which the head/slider is pushed against the recording surface of the magnetic disk, and an air bearing surface of the slider is balanced with buoyancy which the air bearing surface undergoes from a current of air created on the surface of the magnetic disk, whereby a predetermined gap is ensured between the air bearing surface and the recording surface.
While the magnetic disk rotates at a predetermined number of revolutions, the slider and the recording surface of the magnetic disk scarcely contact each other under the action of an air current created on the disk surface. However, if the head/slider lands on the recording surface of the magnetic disk whose rotation has stopped, the head/slider is attracted to the recording surface of the magnetic disk due to, for example, a lubricant applied to the recording surface, inter-attraction between smooth surfaces of the recording surface and the air bearing surface, and pressure of the load beam. If the magnetic disk is rotated in the attracted state of the head/slider, a phenomenon called sticktion will occur, which may flaw the surface of the slider or the magnetic disk or may result in start-up being impossible. If the number of revolutions of the magnetic disk lowers to a level below a predetermined value, the buoyancy between the slider and the recording surface decreases and both come into contact with each other, with consequent likelihood of damage. Therefore, it is also necessary to prevent such a decrease in the number of revolutions of the magnetic disk.
Thus, in the load/unload type magnetic disk drive, at the time of stopping the rotation of the magnetic disk, the head/slider is retracted to a retracting position called ramp which is provided outside the recording surface of the magnetic disk, then the magnetic disk is started up and the head/slider is held in the ramp until the rotation of the magnetic disk becomes a normal rotation. In the load/unload type magnetic disk drive there is provided an outer crash stop formed of an elastic material such as rubber to define a limit position of a pivotal range when the actuator assembly moves pivotally toward the retracting position.
In a normal retracting motion of the actuator assembly, the actuator assembly is moved pivotally at a controlled speed from the recording surface to the retracting position until light collision with the outer crash stop to turn OFF a voice coil motor (VCM). The outer crash stop attenuates a shock energy of the actuator assembly, causing the actuator assembly to stop at the retracting position which lies above the ramp. When the magnetic disk is next rotated and the head/slider is moved to the recording surface, it is necessary that the actuator assembly be held at such a degree of strength as permits it to turn quickly with the driving force of VCM. In other words, it is necessary to avoid fixing it firmly at the retracting position.
On the other hand, while the magnetic disk drive is carried alone or in a mounted state onto a portable device, it may undergo a shock comprising various parameters such as strength, angle, position, and rotation from the exterior. Such a shock from the exterior may cause the head/slider to move to the recording surface of the magnetic disk which is at a standstill, giving rise to sticktion. Further, in the event of sudden power failure while the magnetic disk drive operates and the head/slider is making access to the recording surface of the magnetic disk, the actuator assembly is moved to the retracting position by utilizing a counter-electromotive force of the magnetic disk which is rotating or by utilizing an electric charge stored in an electronic circuit to prevent the occurrence of sticktion.
In this connection there is adopted a circuit configuration wherein the speed of the actuator assembly becomes fairly higher than the normal retracting speed in order to permit positive retraction with limited energy. After collision of the actuator assembly with the crash stopper, the actuator assembly may rebound and the head/slider may return to the recording surface of the magnetic disk whose number of revolutions is in a lowered state below a predetermined value.
Further, since a control circuit is constructed so that even when control of the actuator assembly becomes impossible during operation, this state is detected and the head/slider is moved immediately up to the retracting position, there may occur a phenomenon similar to the above. For example, in WO 00/74056, there is described a technique for holding the actuator assembly in the retracting position so as not to rebound and move to the operation range even in the event of violent collision thereof with the stopper.
In FIG. 8 of WO 00/74056 there are shown a lever 15 which is supported pivotably about a pivot shaft 18 and a latch 16 having an engaging concave 15b and an engaging side portion 15c both capable of engaging with operating pins 16a and 16b of the lever 15, the latch 16 being supported pivotably about a pivot shaft 19. When an actuator arm 6 undergoes a strong shock and moves pivotally in C1 direction and tends to move pivotally in B1 direction as a reaction of collision with an outer crash stop 17, a sensor projection 16e formed in the latch 16 is pushed by the actuator arm and causes the latch 16 to move pivotally in B3 direction, thereby preventing the latch from jumping out from its home position.
A rotating disk storage device having a rotating disk storage medium undergoes a shock defined by various parameters from the exterior while it is in operation and not in operation. Against such a shock it is necessary to prevent the head/slider from landing on the recording surface of the recording medium which is at a standstill or is rotating at a speed below a predetermined number of revolutions. This is also true of the case where the control of an actuator head suspension assembly (hereinafter referred to simply as “AHSA”) becomes unstable or the case where there occurs runaway thereof or where the supply of electric power stops suddenly during operation.
For restricting the pivoting range of AHSA, the storage device is provided with an outer crash stop and an inner crash stop on both sides of the pivoting range, both outer and inner crash stops being formed of an elastic material. In a load/unload type storage device using a ramp, an AHSA is brought into collision with the outer crash stop when retracted to attenuate collision energy and is stopped at a position close to the outer crash stop, allowing a head/slider to be retracted to the ramp. However, it is impossible for the outer crash stop to fully attenuate the collision energy of the AHSA which collides with the outer crash stop at a high speed. Moreover, the selection of an elastic material and temperature management are difficult. Thus, it is not easy to control the attenuating action. Particularly in an ultra-small sized rotating disk storage device such as a one-inch type, the space for provision of an elastic member is restricted and there occurs a great temperature change. Therefore, it is not easy to let an elastic effect of such an elastic member as rubber be exhibited appropriately.
Further, in the method disclosed in WO 00/74056, there is a fear that a latching shock may exert a bad influence on AHSA as the latching frequency for AHSA increases. The AHSA is constructed of precision parts for obtaining a satisfactory follow-up characteristic of head/slider, so there is a fear that the characteristic may deteriorate as the latching shock increases. Therefore, in a latch mechanism for latching AHSA after collision with the outer crash stop and rebounding, it is desirable to minimize the latching frequency and fully attenuate AHSA energy when latching. For this reason it is desired to provide a mechanism to let AHSA be retracted to the retracting position without giving a shock thereto against external shock, runaway during operation, or power failure.